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Most countries in the world now use the metric system. Almost the only holdouts still using the old British Imperial system of weights and measures are the USA and Liberia (and Burma which uses yet another system). The United Kingdom and Canada (except the already fully metrified francophone Quebec) are in a curious state halfway between metric and Imperial units, and while many things are measured in metric, you will still often encounter miles, pints, feet and stone during your visit. The only units the two systems have in common are time units from second to century.

We use "=" signs below, but all are approximate.

Temperature

←freezing

cold

cool

mild

warm

hot

swelter

cooked→

°C

-40

-18

-4

0

4

7

10

13

15

18

21

24

26

30

32

35

40

°F

-40

0

25

32

40

45

50

55

60

65

70

75

80

85

90

95

104

100 °C — 212 °F — Water boils

58 °C — 136 °F — Highest temperature recorded on Earth

37 °C — 98.6 °F — Human body temperature

20 °C — 68 °F — Room temperature

0 °C — 32 °F — Water freezes

-18 °C — 0 °F — Ouch. Finnish people start to wear jackets.

-40 °C — -40 °F — Forty below zero!

-89 °C — -129 °F — Lowest temperature recorded on earth

-273.15 °C — -459.67 °F — Absolute zero

For those who are not used to Metric thermometers, there are a few ways to think about it...

Option 1: From Metric (Celsius) to Fahrenheit, double the number and add 30. From Fahrenheit to Celsius, subtract 30 and divide in half. This is not exact and it won't work for much higher or lower temperatures, but it will be close enough to understand what the temperature is.

Option 2: A nice little poem to remember for Celsius...
Zero is freezing
10 is not
20 is warm
and 30 is hot

Option 3: For the mathematically inclined or those with a calculator: Fahrenheit=(C*1.8)+32. Celsius=(F-32)/1.8

Weight

Surface area

For small things, one might use square inches or square centimeters. There are about 6.5 cm2 in one in2.

For floor area of an apartment, there are about 11 square feet in one square meter.

For large areas, there are about 2.5 acres in one hectare.

Volume

The standard metric unit of volume is the litre.

Many things, however, are measured in ml (millilitres) or equivalently in cc (cubic centimetres). Roughly, a teaspoon is 5 cc and a fluid ounce is 30 cc.

In both the US and Imperial systems, 4 quarts = 1 gallon and 2 pints = 1 quart. However, the US units are smaller than Imperial counterparts. A US quart is 32 fluid ounces while Imperial is 40; a litre is in between at 35. A US gallon is 128 ounces or 3.78 litres, while an Imperial gallon is 160 ounces or 4.54 litres.

For car and motorcycle engines, displacement might be given in cc or litres or cubic inches. 1000 cc or one litre is 61 cubic inches.

Comparisons

1 L of water weighs 1 kg. Since many liquids (milk, orange juice) are sold in litre containers it is easy to judge 1 L or 1 kg.